Nail It Up, Call It a Problem
Eric, one of the owners of Hansen Pole Buildings, was contacted by a prefabricated roof truss manufacturer recently. They weren’t interested in selling just trusses; they wanted to provide their nail-laminated posts as well.
Among their selling points were the columns were, “stronger than even the glu-laminated columns”. They Emailed to Eric some nice glossy literature, which Eric forwarded to me, knowing how I love to pick things apart.
The first thing I noticed is, their literature is using values for the #2 Southern Yellow Pine (SYP) 2x6s, which their columns are made from, based upon the 1997 NDS (National Design Specification). However, the strength values for dimensional SYP have been downgraded as of June 1, 2013. This means the values listed in their literature are 25% too high in bending and about 15% in compression!
As manufactured by this company, the #2 SYP is used for the bottom pressure treated portion of the column, and the upper is #2 SPF (Spruce-Pine-Fir). The SPF has an Fb (fiberstress in bending) value of 1138 psi (pounds per square inch) compared to an Fb of 1000 for the 2×6 SYP.
Interestingly, the company DOES only take credit for the section modulus (Sm) in the spliced are as being 2/3 of what three 2×6 unspliced would provide. AS we will soon prove, this 2/3 is being pretty generous to them.
Dr. Frank Woeste’s “Nail Laminated Wall Columns from Dimensional Lumber” (see TRANSACTIONS of the ASAE Volume 27, Number 4, pp. 1127-1130, 1984) compared the strength of nail-laminated posts, with internal non-reinforced butt end splices.
In Woeste’s testing three-ply 2×6 #2 Dense SYP nail laminated posts, were compared in strength to 6×6 #2 SYP solid sawn columns. The moment resisting ability of a wood member is calculated from Fb X CD (duration of load = 1.6 for wind) X CM ( = 0.85 wet service factor for dimensional lumber) X Cr (repetitive member factor for 3 members joined together) X Sm. As the testing was done on lumber which had not been subjected to moisture CM will be disregarded for comparisons.
For 2×6 #2 Dense SYP (based upon 1985 values) 1450 X 1.6 X 1.15 X 3 members X 7.5725 = 60,530 in-lbs. For 6×6 #2 SYP 850 X 1.6 X 27.73 = 37,712 in-lbs. Therefore, the 3 2×6 (no splices) would be 60% stronger than the solid sawn 6×6.
In the study, using the butt spliced columns, the 3 2×6 #2 Dense turned out to be only 64% as strong as a 6×6! Whoops…..
Using the results of this scientific study, it would appear non-reinforced butt spliced columns should probably be used at a value of somewhere around 40% of the strength of non-spliced columns. While I know there are some folks (those who use or produce the non-reinforced butt spliced columns) who are not going to like to read this – the facts are indisputable.
A better place to look for the values of nail laminated columns that are spliced is ASABE 559.
NDS does does not allow a mechanically fastened column to be spliced so anybody publishing values for them based upon NDS are making a mistake.
There are a number of nail laminated columns being manufactured that have higher design values in braced applications than glulams.
Thank you very much for following my postings. ASABE 559 does indeed give some insights into the design values for nail laminated columns, however the user should be wary. The majority of glulaminated columns (e.g. manufacturers such as Gruenwald Engineered Laminates and Timber Technologies) are producing a product out of 1650 Fb rated materials. According to ASABE 559, they would be able to use Cr of 1.25 for a three ply mechanically graded lumber, giving a net Fb before other adjustments of 2062.5.
Let’s take a look at a nail laminated column, butt end spliced, manufactured from three 2×6 #2 SYP. The base Fb value is 1000 psi. ASABE 559 provides for a Cr of 1.35 for 3 ply, visually graded material. ASABE 559 also gives (in Table 8) an adjustment factor for nail-laminated assemblies, where Fb is multiplied by 0.42 for non-reinforced splices (provided proper assembly has been done per ASABE 559). Using Cr and the adjustment factor gives the resultant Fb of 567, or just under 28% of the strength of a the glulaminated columns referenced.
Please feel free to share data on the higher strength nail laminated columns.
ASABE 559 is only for a Mechanically laminated column, not glu-lams so the increased repetitive bending factors found in it cannot be used for a glulam. Glulam manufacturers have ANSI 190.1 or NDS as a means of providing values for their laminated columns.
Mechanically laminated columns with Structural Finger Joints have a section modulus that is roughly 15% greater than a glulam that has been sized according to the glulam standards.
That additional 15% of SM plus the added repetitive bending provided by ASAE 559 will give you a column with a design value significantly higher than an equivalent glulam column in a braced application.
Bob ~ Let’s take a look at reality….
A 3ply 2×6 glulam has a Sm of 19.86, as a product of 1650 Fb lumber 19.86 X 1650 X 1.15 Cr = 37,688.7
A 3ply mechanically laminated column has an Sm of 22.6875, as a product of 1000 Fb (2×6 #2 SYP) gives 22.6875 X 1000 X 1.35 Cr = 31,710.8
This still leaves the glulam column nearly 19% greater in strength than the mechanically laminated column with structural fingerjoints. It would take visually graded lumber with an Fb of at least 1189, just to be equivalent in strength to the glulam. Using #1 SYP would give a product which is stronger than the glulam.
I should have stated that both column use the same material in my example above. That has become standard for most laminated column manufacturers at this point in time.
You are saying you are using Fb = 1650 product (or better) to manufacture your columns?
Yes.In the upper. M29 SYP in the lower
Bob ~ As the great majority of my readers are unfamiliar with Mechanically Graded Dimension Lumber I will give them some idea as to its properties. M-29 is a grade for Machine Evaluated Lumber (or MEL). M-29 has a fiber strength in bending (Fb) of 1550 psi. In theory, your product SHOULD be stronger, however theory and reality are not often the same. I’d direct my readers to this video, where they can come up with their own conclusions: https://www.youtube.com/watch?v=91nUG_n4Hwk
I’d remind anybody viewing that type of video to keep in mind that legitimate comparative testing of any product requires that it be done by a third party in a certified laboratory, with very stringent criteria regarding the materials being used as well as the fabrication surrounding the samples being tested.
I’ve done the same tests in a 3rd party laboratory with signficantly different results. Tests such as these can be affected (intentionally or unintentionally)by a variety of factors that are not observable or understood by simply watching an edited video.
The reason that Standards such as ANSI 190.1 (glulam) and ASABE 559 (mechanical fastenters) are developed by third party groups or associations is to insure objectivity to the consumer and prevent bias that is inherent to all manufacturers.
Could you share the results of the third party testing done on your products Bob? I am certain our readers would find them to be fascinating.
They were done by me in a third party laboratory so they don’t meet the full criteria of third party testing. I did them in order to provide our management internal data regarding the performance of multiple products, one which is ours. In my opinion, it’s irresponsible to release it for that reason. I can tell you that our test results correlated with test results done in the Forest Products laboratory as well as the tests done to create ASABE 559. The results shown in the video do not.
Bob ~ Maybe you and the manufacturers of Titan Timbers need to agree upon a set of testing parameters and have a “bust off” to once and for all determine who has the stronger product?
Frankly, I don’t know who’s column they tested so I see no need in doing a comparitive test between our and theirs.
Our goal is to manufacture products that meet I-code approved standards and allow those products to fall under the umbrella provided by those codes. In our case, it’s ASABE 559, which was originally developed over 10 years ago specifically for the Post Frame industry. The numbers we publish are a result of hundreds of columns tests, not 10 pieces.
There is nothing magical that happens when a randomly selected piece of visually graded Southern Pine is glued that makes it stronger than it’s published values. That the lumber industry found it necessary to reduce the values of visually graded SP is the result of destructively testing many thousands of pieces of randomly selected lumber using scientifically significant methods if testing. The values we publish are a result of those tests along with hundreds of columns tests, not 10 pieces.
In my humble opinion only – if one of my competitors threw down the glove and challenged me to a smack down, and I truly believed my product was better, I’d be taking them up on the “bust off” to shut them up once and for all.
One thing readers may want to note – there must be something “magical” about nailing up three pieces of lumber to use a Cr value of 1.35 (which Bob is using) as opposed to the glu-laminated columns which are using a Cr of 1.15. I am not blaming Bob personally for hanging his hat on a system which allows him to get credit for supposedly being over 17% stronger, when the difference is between plies being nailed together or structurally glued.
Clearly I did not make my point clear so I’ll rephrase it for clarity. Using identical repetitive bending’s, the nail laminated column still has a section modulus (22.69) that is 14% greater than the equivalent glu-lam (19.92). Therein lies the difference.
In addition to being a manufacturer of nail laminated columns, we also are a distributor of Timber Technologies Glue laminated columns. It is a very good column. But in the end it has less section modulus than an equivalent nail laminated column. That is a simple fact of engineering.
I don’t know of any nail laminated column manufacturer that makes the claim that nails are stronger than glue. They are not. Nor is glue stronger than nails in the strong axis. By design they both allow the lumber to achieve it’s full design value.
As always Guru your knowledge and passion for the industry is commendable. I always appreciate your loyalty to glue lam columns.
Since I felt the urge to respond to the blog concerning treated gluelams from 2012, I guess I regarded my input as somewhat relevant on this one. Though I am trying to be careful not to get bogged down posting considering my time constraints. All this talk about standards is riveting. Yawn.. Nail Lam manufacturers have always claimed to follow the ASAE 559. Some even do, and I have no doubt the product Mr Mochinski represents does. I have read and reviewed many of the standards published by ASAE over the years. The one I like best is how to make plywood gusset trusses, but let’s stay focused on columns shall we. There may be several points that need clarifying. Mr Mochinski claims that there were hundreds of columns tested to determine the Cr factor for nail lam columns. In every test I reviewed the sample size is 25 or less. Another concern would be applying the 1.35 Cr factor when it states in the 559 Standard a Cr for mechanically graded material is 1.25, which MSR 1650 and M29 fall into. Misusing the factors could be the difference between falling down and standing up, so I feel it is best to clarify. Though I am aware that 559 was being reviewed last summer and I do not have a copy of the latest version.
In the end all this discussion about standards, factors, and third party testing and design values is really exciting. Our position here at Timber Technlogies on this matter has not changed. We have the equipment to run a head to head comparison at our testing facility. I am sure Mr Mochinski and I could find common ground on how to make it as fair as possible to both parties. Rest assured whatever the results, they will be made public.
Dale ~ Thank you for your excellent response. I’m hopeful Mr. Mochinski will take you up on your offer – as it would certainly put to rest what the actual product strengths are. If the challenge is taken, I’d suggest each party place a representative in the plant of the other party during manufacturing, as it would be all too tempting for someone to (totally by accident) grab some higher graded lumber and have it incorporated into their columns. I’d think this would be especially crucial in the case of the nailed up columns – where the center ply is carrying more than 1/3 of the load (due to the nailing from each side).
You are also correct on the Cr (at least as it in the Standard you and I both have copies of), where the lesser variability of machine rated lumber results in only being able to utilize the lesser value.
Below are just two of the many tests conducted on nail laminated columns. Just these two tests had 215 columns tested to destruction. There are a number of tests that have been done all the way back to 1966 (Bonnickson and
Suddarth 1966) that have provided the foundation for the development of ASABE 559.
75 4 ply columns were tested
140 3 ply columns were tested
Assuming that Cr is the same for both columns (as I believe it should be) there is still a difference in Section Modulus of 14%. That is a mathematical fact guys and there is nothing in any type of fastener be it glue, nails, bolts, screws or anything else that changes that fact.
To be clear, I have no issue with glue laminated columns. We sell them and recommend them over nail lams in a number of applications. However, the design values provided by ASABE 559, which have been accepted by the International Building Code, clearly provide a design value in a braced application that is greater than the equivalent glulam column, regardless of who manufactures them. And the values provided are backed by numerous tests done by objective third party organizations. I’d suggest you review page 4 of the document below (Lumber selection and allocation) to truly understand how an objective comparitive test needs to be conducted. To be meaningful, it’s a bit more involved than you may believe. https://www.fpl.fs.fed.us/documnts/fplrp/fplrp528.pdf
Any manufacturer who believes they have a product that is superior to what is provided by Code Approved Standards would find their time and money better spent on getting a code approval for that product than in-house comparative testing as that provides objective proof to the consumer about the superiority of their product.
Our goal for all of our products is assurance to our customers that they meet or exceed the current building code standards. We believe that the objectivity provided by them is the best guarantee for the end user.
Assuming lumber grades were exactly equal and Cr values were exactly equal, then the only issue to address from an “on paper” standpoint would be the size of the section – and a column fabricated from member which were not planed, would have a larger section and theoretically be stronger (given properly finger jointed splices). I don’t believe anyone can disagree.
I’ve personally been involved in the testing of nail laminated columns – at the Oregon State University Forest Products lab. From this experience…..unless the nails being used were to be all the thickness of the entire assembly, the middle member of the nail laminated column will fail first nearly every time. Why? Because there are more fasteners into it (or more length of fasteners). Will they fail within the design parameters – highly unlikely. Glue laminated columns do not have the fastener issue.
Nail laminated columns are three distinct individual members, mechanically fastened. A glue laminated column becomes an individual member and functions as one. This is why nail laminated columns can not be used in an unbraced condition – as in columns on an open sidewall, side shed or carport – they buckle in the weak direction.
When I personally design a building for a client, I design it as if it was going to be a building for my own personal use. I recommend products based upon how I know they actually perform, not necessarily how some table and adjustment factors tell me they should perform. Without trying to come across as offensive, there are very few scenarios I can envision where I could, in good faith, recommend a nail laminated column over a glue laminated column.
In my humble opinion only – you’ve got the hardest part of the glue laminated process down Bob – you can produce quality finger joints. My recommendation would be to take things a step further and invest in the equipment to produce true glue laminated columns. There is more demand for them than what is available in the marketplace, and the value added should certainly make for an entirely more profitable bottom line.
Mechanically fastened columns can be used in unbraced applications though there are design value reductions about the weak axis. We recommend glulams to our customers in those cases as we believe they are the best product for that condition when a Registered Design Professional is not designing the structure. In many of the cases where there is a Registered Engineer, we see them use nailed columns in unbraced applications as they provide the best strength to cost ratio in a laminated column.
No need for us to make a glulam as there are a number of very good suppliers such as Timber Technologies in the market place already.
I am a pole barn builder in Connecticut I have been building barns since 1990 I’ve had no failures to a 3-ply nailed pressure treated post I even put buildings in Massachusetts in New York the same way this past week in the town of Groton Connecticut I was told it was not sufficient for a nailed post I had to go to an engineer and he allowed me to do 4 ply with 8 inch on Center quarter by 6 screws staggered each side that was on the bearing wall I personally think we are just getting out of control with codes if things have been working for nearly 30 + years I don’t get it
While I can appreciate your no failure track record, it does not necessarily mean it can be proven on paper – hence the requirement for engineering. From the aspect of a builder, having the entire building fully engineered protects you from liability in the event of a failure as well as being a distinct selling point against your competitors.
Unless you are building moment resisting frames, all of this discussion about bending stress is irrelevant. A column is a structural member loaded along the longitudinal axis of the member. A beam is loaded perpendicular to the longitudinal axis. Bending stress values are for beams. A properly braced frame should have little bending stress to resist.
Post frame building columns are subjected to both axial compression and bending moments.